1. Field of the Invention
The present invention relates to hard copy media control apparatus. More specifically, the present invention relates to method and apparatus for control of paper in a cut-sheet paper feeding mechanisms for use with printers, plotters, copiers, facsimile machines and the like.
2. Description of the Related Art
Paper feed mechanisms for hard copy control apparatus are well known in the art. In automatic cut sheet printers, a stack of paper is automatically fed to a printer, plotter, copier, facsimile machine, or other apparatus typically using a roller assembly or other mechanism. An important function of the feed mechanism is to control the parallelism between the top edge of the sheet of paper and the first line of print contained thereon, i.e., the amount of skew between the paper and the print. Even a small amount of skew between the paper and print will cause the printing to appear crooked. Larger amounts of skew may cause buckling of the paper, resulting in uneven print quality or jamming of the paper within the printer. The skew is generally induced when the paper is loaded into and/or picked from a stack of paper in a supply tray. Accordingly, it is desirable to minimize the amount of skew between the paper and the printing assembly once the paper has been picked and before it is printed on.
Prior art printing devices use a variety of techniques and apparatus to minimize skew. Some minimize skew by forcing a sheet of paper into a pair of stalled rollers, creating a buckle in the paper and forcing the leading edge of the paper to be parallel with the roller pair. The rollers are then activated to advance the paper into the print zone. Such a technique requires some type of clutching mechanism to stall the rollers long enough to allow the paper to be fed into the nip between the rollers. Further, this technique requires accurate control of the paper while it is buckling, as the buckle must be large enough to correct the skew, yet small enough that the paper does not flip out of the nip between the stalled rollers. Other prior art devices use tapered rollers which direct the sheet of paper against a reference wall, forcing it into alignment therewith and eliminating any skew before printing. This technique requires a large, flat surface in the area of the roller assembly and is relatively slow. Still other devices have no skew correction mechanism at all, relying entirely on the accurate feeding of paper into the roller assembly.
In addition to minimizing skew, the feed mechanism must maintain accurate control of each sheet, from the time it is picked from the stack until it is ejected from the apparatus. The paper feed mechanisms of typical prior art printers, plotters copiers, facsimile machines and the like use separate motors and gear arrangements to pick the paper from a stack, deliver the paper to a printing assembly, line feed the paper and eject the paper once printed. Such feed mechanisms often encumber the carriage drive motor and have complex timing schemes requiring triggering devices, such as solenoids. The large number of motors and other electrical components increases the cost of the apparatus. Further, complex feed mechanisms increase the amount of time necessary to pass a page through the apparatus, as well as the chances of paper jams and skew errors.
The need in the art for a sheet feeding mechanism having a minimal number of control devices was addressed to some extent by U.S. Pat. No. 5,226,743 issued Jul. 13, 1993 to Jackson et al. and entitled METHOD AND APPARATUS FOR PAPER CONTROL IN A PRINTER, the teachings of which have been incorporated herein by reference. This reference discloses and claims an apparatus for control of a sheet of paper in a printer mechanism including a single motor drive mechanism, a frame, a platen, a roller assembly for advancing sheet of paper over the plates, and a kicker element for selectively contacting only an edge of a sheet of paper and for urging the sheet of paper in a forward direction once it is disengaged from the roller assembly.
Notwithstanding the benefits associated with the design set forth in the above-referenced patent, a need remains in the art for further improvements in sheet feed mechanisms which afford reliable, accurate control of paper through an apparatus with high throughput at low cost. This is particularly true with respect to the role of the kicker.
Kickers are used to assist in the movement of paper in sheet feeding mechanisms. For example, a kicker may be used to assist in the movement of a printed page into a receiving tray as disclosed in the above-identified Jackson patent. In the alternative, kickers may be used to reset stacks of paper in a sheet feeder during a printing operation so that the printing of each sheet starts from a known initial state.
Currently, many sheet feeding mechanisms are known in the art. Typically, sheet feeding is accomplished using a roller on top of the paper and a friction pad on the bottom. In this application, the kicker assists in the movement of paper out of the nip area between the roller and the pad to prevent multi-feeds.
Unfortunately, conventional kicker mechanisms require many parts and are therefore costly and require a considerable amount of space. Hence, a need remains in the art for an inexpensive yet effective kicker mechanism for the next generation of hard copy apparatus.